'\" te
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.TH PORT_ALERT 3C "April 9, 2016"
.SH NAME
port_alert \- set a port in alert mode
.SH SYNOPSIS
.LP
.nf
#include <port.h>

\fBint\fR \fBport_alert\fR(\fBint\fR \fIport\fR, \fBint\fR \fIflags\fR, \fBint\fR \fIevents\fR, \fBvoid *\fR\fIuser\fR);
.fi

.SH DESCRIPTION
.LP
The \fBport_alert()\fR function transitions a port into or out of alert mode.
A port in alert mode immediately awakens all threads blocked in
\fBport_get\fR(3C) or \fBport_getn\fR(3C). These threads return with an alert
notification that consists of a single \fBport_event_t\fR structure with the
source \fBPORT_SOURCE_ALERT\fR. Subsequent threads trying to retrieve events
from a port that is in alert mode will return immediately with the alert
notification.
.sp
.LP
A port is transitioned into alert mode by calling the \fBport_alert()\fR
function with a non-zero \fIevents\fR parameter.  The specified \fIevents\fR
and \fIuser\fR parameters will be made available in the \fBportev_events\fR and
the \fBportev_user\fR members of the alert notification, respectively. The
\fIflags\fR argument determines the mode of operation of the alert mode:
.RS +4
.TP
.ie t \(bu
.el o
If \fIflags\fR is set to \fBPORT_ALERT_SET\fR, \fBport_alert()\fR sets the port
in alert mode independent of the current state of the port.  The
\fBportev_events\fR and \fBportev_user\fR members are set or updated
accordingly.
.RE
.RS +4
.TP
.ie t \(bu
.el o
If \fIflags\fR is set to \fBPORT_ALERT_UPDATE\fR and the port is not in alert
mode, \fBport_alert()\fR transitions the port into alert mode.  The
\fBportev_events\fR and \fBportev_user\fR members are set accordingly.
.RE
.RS +4
.TP
.ie t \(bu
.el o
If \fIflags\fR is set to \fBPORT_ALERT_UPDATE\fR and the port is already in
alert mode, \fBport_alert()\fR returns with an error value of \fBEBUSY\fR.
.RE
.sp
.LP
\fBPORT_ALERT_SET\fR and \fBPORT_ALERT_UPDATE\fR are mutually exclusive.
.sp
.LP
A port is transitioned out of alert mode by calling the \fBport_alert()\fR
function with a zero \fIevents\fR parameter.
.sp
.LP
Events can be queued to a port that is in alert mode, but they will not be
retrievable until the port is transitioned out of alert mode.
.SH RETURN VALUES
.LP
Upon successful completion, 0 is returned. Otherwise, -1 is returned and
\fBerrno\fR is set to indicate the error.
.SH ERRORS
.LP
The \fBport_alert()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEBADF\fR\fR
.ad
.RS 10n
The port identifier is not valid.
.RE

.sp
.ne 2
.na
\fB\fBEBADFD\fR\fR
.ad
.RS 10n
The \fIport\fR argument is not an event port file descriptor.
.RE

.sp
.ne 2
.na
\fB\fBEBUSY\fR\fR
.ad
.RS 10n
The port is already in alert mode.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
Mutually exclusive \fIflags\fR are set.
.RE

.SH ATTRIBUTES
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Architecture	all
_
Interface Stability	Evolving
_
MT-Level	Safe
.TE

.SH SEE ALSO
.LP
.BR port_associate (3C),
.BR port_create (3C),
.BR port_get (3C),
.BR port_send (3C),
.BR attributes (7)
